1. Field of the Invention
The present invention relates to a safety injection system capable of injecting coolant to a reactor coolant system when a loss-of-coolant-accident (LOCA) occurs on an integral type reactor.
2. Background of the Invention
An integral type reactor has a characteristic that large pipes connected with main components such as a core, steam generators, a pressurizer, and pumps are not required, because the main components are installed in a reactor vessel. Pipes configured to connect a chemical and volume control system, a safety injection system, a shutdown cooling system, a safety valve, etc. with the reactor vessel of the integral type reactor are small. As the main components are accommodated in the integral type reactor, a great amount of coolant for a reactor coolant system is provided at an inner space of the reactor coolant system.
In the occurrence of a loss-of-coolant-accident (LOCA), this is a small break-loss-of-coolant-accidents (SBLOCA) due to a pipe rupture, etc., the integral type reactor shows progress states different from those of a separate type reactor. In case of the separate type reactor provided with large pipes, coolant is drastically lost when the large pipes are ruptured. Further, as the coolant is discharged, the reactor is drastically depressurized for a rapid pressure equilibrium state between the reactor and a reactor building (or containment). As a result, safety injection by a gravitational head of water is facilitated, and the coolant is rapidly refilled into the reactor by a safety injection system. Unlike such separate type reactor requiring a rapid injection, the integral type reactor has a characteristic that pressure and level thereof are gradually lowered when a loss-of-coolant-accident occurs, because large pipes are eliminated. As a result, a pressure equilibrium state between the reactor and a reactor building cannot be rapidly implemented, and there is a difficulty in performing safety injection by a gravitational head of water.
In order to solve such problems, the integral type reactor has been configured to adopt a safety injection tank using pressurized gas (generally, nitrogen) to inject coolant, or configured to comprise a specified passive safety injection system using a high pressure small containment. The passive safety injection system is configured to restrict the amount of coolant to be discharged by rapidly making a pressure equilibrium state between the reactor and a safeguard vessel, using a high pressure small containment such as a safeguard vessel, rather than a reactor building. The passive safety injection system uses a gravitational head of water, or a gas pressure, etc.
A safety injection tank, one of the passive safety injection system, especially, an integral type safety injection tank configured to inject coolant using pressurized gas and having coolant and gas stored in a single tank, is very sensitive to a pressure change inside a reactor coolant system in the occurrence of a LOCA.
In the occurrence of a large-break-loss-of-coolant-accident (LBLOCA), the reactor is drastically depressurized, safety injection is performed within a short time as coolant is rapidly injected. On the other hand, in the occurrence of a small LOCA, the reactor is gradually depressurized to cause safety injection not to be performed when required.
In the safety injection tank configured to pressurize coolant using gas, if a reference pressure is set to be lower than a reactor pressure predicted in a large-break-loss-of-coolant-accident, coolant may not be safely injected into the reactor when a small-break-loss-of-coolant-accident occurs, because the reactor is little depressurized. On the other hand, if the reference pressure is set to be higher than the reactor pressure predicted in a small-break-loss-of-coolant-accident, a safety injection operation may be early terminated when a large-break-loss-of-coolant-accident occurs, because the reactor is rapidly depressurized.
Accordingly, may be considered a safety injection system capable of injecting a comparatively constant amount of coolant regardless of a scale of a pipe rupture.